The present invention relates generally to well drilling operations and, more particularly, to well drilling operations using magnetic ranging to drill multilateral wells.
Heavy oil is too viscous in its natural state to be produced from a conventional well. To produce heavy oil, a pair of Steam Assisted Gravity Drainage (SAGD) wells may be employed, which use superheated steam to heat heavy oil until its viscosity is low enough to be produced. A SAGD well pair includes two parallel horizontal wells which generally remain separated by an approximately constant vertical separation distance (e.g., 4 to 6 m) over a horizontal distance of roughly 500 m to 1500 m.
The upper well in a SAGD well pair is known as an “injector welt” The injector well injects superheated steam into a heavy oil zone formation, creating a steam chamber to heat the heavy oil contained therewithin. The lower well in a SAGD well pair is known as a “producer well.” When the heated heavy oil becomes less viscous, gravity pulls the oil into the producer well below, from which the oil may be extracted.
Conventional measurement while drilling (MWD) survey data does not provide sufficient accuracy to maintain a consistent separation distance between the injector well and the producer well. Instead, conventional magnetic ranging may be employed to drill the second of the two wells of a SAGD well pair. With conventional magnetic ranging techniques, a wireline tool is placed in the first well while the second well is drilled. A magnetic field between the wireline tool in the first well and a bottom hole assembly (BHA) in the second well allows the BHA in the second well to maintain an accurate vertical separation distance between the first and second wells of the SAGD pair.
To reduce environmental impact at the surface, and for economic reasons, many non-SAGD wells employ a single mother wellbore having one or more multilateral junctions. The multilateral junctions allow multiple lateral wells to extend from the mother wellbore beneath the surface, which may increase oil recovery while reducing costs. However, multilateral junctions cannot be used with SAGD wells drilled using conventional magnetic ranging techniques. Since conventional magnetic ranging techniques involve placing a wireline tool into the first well of a SAGD well pair while the second well is drilled, the wireline associated with the wireline tool would be present alongside the drill pipe in the mother well. As such, the wireline could become wrapped around or crushed by the drill pipe, and cuttings from the second well could enter the first well and trap the wireline tool.